Cooperative link characterization and MCS selection by wireless terminal and network for improved system performance

ABSTRACT

RF communications received by a wireless terminal from a servicing base station are used to determine the downlink quality report and implement link adaptation decisions. This involves first implementing an initial transmission scheme between the servicing base station and the wireless terminal. Next, a current downlink quality report corresponding to the initial transmission scheme is generated by the wireless terminal and received at the servicing base station. This downlink quality report is based in whole or in part on a bit-error probability (BEP). The current downlink quality report that corresponds to the initial transmission scheme is then compared to link adaptation thresholds. When the current downlink quality report compares unfavorably to the link adaptation thresholds, an alternative transmission scheme is selected and implemented between the servicing base station and the wireless terminals if the alternative transmission scheme is expected to result in an improved downlink quality report over the current down-link quality report.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional PatentApplication Ser. No. 60/478,922, filed Jun. 16, 2003, which isincorporated herein by reference for all purposes.

BACKGROUND

[0002] 1. Technical Field

[0003] The present invention relates generally to cellular wirelesscommunication systems, and more particularly to the determination of abit error probability of radio frequency communications received by awireless terminal within a cellular wireless communication system.

[0004] 2. Related Art

[0005] Cellular wireless communication systems support wirelesscommunication services in many populated areas of the world. Whilecellular wireless communication systems were initially constructed toservice voice communications, they are now called upon to support datacommunications as well. The demand for data communication services hasexploded with the acceptance and widespread use of the Internet. Whiledata communications have historically been serviced via wiredconnections, cellular wireless users now demand that their wirelessunits also support data communications. Many wireless subscribers nowexpect to be able to “surf” the Internet, access their email, andperform other data communication activities using their cellular phones,wireless personal data assistants, wirelessly linked notebook computers,and/or other wireless devices. The demand for wireless communicationsystem data communications will only increase with time. Thus, cellularwireless communication systems are currently being created/modified toservice these burgeoning data communication demands.

[0006] Cellular wireless networks include a “network infrastructure”that wirelessly communicates with wireless terminals within a respectiveservice coverage area. The network infrastructure typically includes aplurality of base stations dispersed throughout the service coveragearea, each of which supports wireless communications within a respectivecell (or set of sectors). The base stations couple to base stationcontrollers (BSCs), with each BSC serving a plurality of base stations.Each BSC couples to a mobile switching center (MSC). Each BSC alsotypically directly or indirectly couples to the Internet.

[0007] In operation, each base station communicates with a plurality ofwireless terminals operating in its cell/sectors. A BSC coupled to thebase station routes voice communications between the MSC and a servingbase station. The MSC routes voice communications to another MSC or tothe PSTN. Typically, BSCs route data communications between a servicingbase station and a packet data network that may include or couple to theInternet. Transmissions from base stations to wireless terminals arereferred to as “forward link” transmissions while transmissions fromwireless terminals to base stations are referred to as “reverse link”transmissions. The volume of data transmitted on the forward linktypically exceeds the volume of data transmitted on the reverse link.Such is the case because data users typically issue commands to requestdata from data sources, e.g., web servers, and the web servers providethe data to the wireless terminals. The great number of wirelessterminals communicating with a single base station forces the need todivide the forward and reverse link transmission times amongst thevarious wireless terminals.

[0008] Wireless links between base stations and their serviced wirelessterminals typically operate according to one (or more) of a plurality ofoperating standards. These operating standards define the manner inwhich the wireless link may be allocated, setup, serviced and torn down.One popular cellular standard is the Global System for Mobiletelecommunications (GSM) standard. The GSM standard, or simply GSM, ispredominant in Europe and is in use around the globe. While GSMoriginally serviced only voice communications, it has been modified toalso service data communications. GSM General Packet Radio Service(GPRS) operations and the Enhanced Data rates for GSM (or Global)Evolution (EDGE) operations coexist with GSM by sharing the channelbandwidth, slot structure, and slot timing of the GSM standard. GPRSoperations and EDGE operations may also serve as migration paths forother standards as well, e.g., IS-136 and Pacific Digital Cellular(PDC).

[0009] The GSM standard specifies communications in a time dividedformat (in multiple channels). The GSM standard specifies a 4.615 msframe that includes 8 slots of, each including eight slots ofapproximately 577 μs in duration. Each slot corresponds to a RadioFrequency (RF) burst. A normal RF burst, used to transmit information,typically includes a left side, a midamble, and a right side. Themidamble typically contain a training sequence whose exact configurationdepends on modulation format used. However, other types of RF bursts areknown to those skilled in the art. Each set of four bursts on theforward link carry a partial link layer data block, a full link layerdata block, or multiple link layer data blocks. Also included in thesefour bursts is control information intended for not only the wirelessterminal for which the data block is intended but for other wirelessterminals as well.

[0010] GPRS and EDGE include multiple coding/puncturing schemes andmultiple modulation formats, e.g., Gaussian Minimum Shift Keying (GMSK)modulation or Eight Phase Shift Keying (8PSK) modulation. Particularcoding/puncturing schemes and modulation formats used at any time dependupon the quality of a servicing forward link channel, e.g.,Signal-to-Noise-Ratio (SNR) or Signal-to-Interference-Ratio (SIR) of thechannel, Bit Error Rate of the channel, Block Error Rate of the channel,etc. As multiple modulation formats may be used for any RF burst,wireless communication systems need the ability to determine whichcoding scheme and modulation format will result in the successfulreceipt and demodulation of the information contained within the RFburst. This decision may be further influenced by changing radioconditions and the desired quality level to be associated with thecommunications.

[0011] Link adaptation (LA) is a mechanism used to adapt the channelcoding schemes and modulation formats to the changing radio linkconditions. LA allows the network to command the handset to change tothe modulation and coding scheme that is best for the current radiocondition while providing a desired level of quality associated with thecommunications. To facilitate LA, an accurate or representative measureof the changing radio conditions is required. The actual Bit Error Rate(BER) associated with the changing radio conditions would provide such ameasure. However, exact BER evaluation is often intractable ornumerically cumbersome. Therefore, approximations or probabilities ofthe BER are sought. Such approximations may be referred to as the BitError Probability (BEP). Methods used to estimate the BEP often rely onadditive white-Gaussian noise (AWGN) to compute the signal to noiseratio (SNR) from which the BEP is based. Although this method is easy toapply, using the standard Gaussian approximation often overestimatessystem performance. Furthermore, such approximations fail to considerwhether or not the RF communications were properly decoded. This overestimation of system performance can result in optimistic BEPs beingused to make LA decisions. LA decisions based upon optimistic BEP canresult in lost communications between the wireless terminal and theservicing base station. Therefore a need exists to implement LAdecisions based on more efficiently determined BEPs.

BRIEF SUMMARY OF THE INVENTION

[0012] In order to overcome the shortcomings of prior devices, thepresent invention provides a system and method to determine the biterror probability (BEP) of a received radio frequency (RF) burst withina data frame and use this information to implement LA decisions thatsubstantially addresses the above identified needs.

[0013] One embodiment involves first implementing a first transmissionscheme between the servicing base station and the reporting wirelessterminal. Next, a first downlink quality report corresponding to thefirst transmission scheme is generated by the wireless terminal andreceived at the servicing base station. This downlink quality reportincludes a bit-error probability (BEP) based on a re-encoded bit-error(RBER) of data within the RF burst and an estimated BEP derived from asingle-to-noise ratio (SNR) of the RF burst. The downlink quality reportalso may include a block error rate (BLER). The first downlink qualityreport that corresponds to the first transmission scheme is thencompared to at least one link adaptation threshold. When the firstdown-link quality report compares unfavorably to the at least one to thelink adaptation threshold, an alternative transmission scheme isselected and implemented between the servicing base station and thewireless terminals when the alternative transmission scheme is expectedto result in an improved expected quality report over the firstdown-link quality report. The downlink quality report may furtherinclude a mean BEP determined by averaging the BEP of each RF burstwithin a data frame and the standard deviation of the BEP within thedata frame.

[0014] A second embodiment includes a cellular wireless communicationsystem having servicing base stations that are operable to select thetransmission scheme for RF bursts (communications) between the servicingbase stations and wireless terminals. At least a portion of the wirelessterminals serviced by the servicing base stations transmits a downlinkquality report on the implemented transmission schemes to the servicingbase stations. This downlink quality report includes a BEP based on theRBER of data within the RF burst and/or the estimated BEP derived fromthe SNR of the RF burst. The downlink quality report also may include ablock error rate (BLER). A link adaptation system operably coupled tothe servicing base station compares the downlink quality report to linkadaptation thresholds. Based on this comparison, the link adaptationsystem implements an alternative transmission scheme between theservicing base station and the wireless terminal when the downlinkquality report compares unfavorably to the link adaptation thresholds.Furthermore, this alternative transmission scheme may only beimplemented when the alternative transmission scheme is expected toresult in an improved downlink quality report over the current downlinkquality report. This downlink quality report may further include themean BEP determined by averaging the BEP of each RF burst within thedata frame and the standard deviation of the BEP. To reduce thepossibility of spurious changes of the transmission scheme, the linkadaptation thresholds may be incremented or decremented when the datawithin the RF burst decoded unfavorably or favorably, respectively.

[0015] Yet another embodiment of the present invention provides a methodto dynamically select a transmission scheme for an RF burst between theservicing base stations and reporting wireless terminals within awireless communication system. A first transmission scheme isimplemented between the servicing base station and the reportingwireless terminal. The reporting wireless terminal generates andtransmits a first downlink quality report corresponding to that firsttransmission scheme to the servicing base station. This down-linkquality report includes a mean BEP determined by averaging the BEP ofeach RF burst within the data frame, a standard deviation of the BEPwherein the BEP is based on an estimated BEP derived from the SNR of theRF burst and an RBER. In the determination of the BEP, the estimated BEPis weighed more heavily when the RF burst decodes unfavorably while theRBER is weighed more heavily when the RF burst is decoded favorably.Should the RF burst decode unfavorably, the RBER may correspond to abit-error-rate exceeding a threshold value. The downlink quality reportis compared to link-adaptation thresholds in order to determine when analternative transmission scheme should be implemented. When the downlinkquality report compares unfavorably to the link adaptation thresholdsand an alternative transmission scheme is expected to result in anexpected downlink quality report being improved over the currentdownlink quality report the alternative transmission scheme may beimplemented.

[0016] Other features and advantages of the present invention willbecome apparent from the following detailed description of the inventionmade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a system diagram illustrating a portion of a cellularwireless communication system that supports wireless terminals operatingaccording to the present invention;

[0018]FIG. 2 is a block diagram functionally illustrating a wirelessterminal constructed according to the present invention;

[0019]FIG. 3 is a block diagram illustrating in more detail the wirelessterminal of FIG. 2, with particular emphasis on the digital processingcomponents of the wireless terminal;

[0020]FIG. 4 is a block diagram illustrating the general structure of aGSM frame and the manner in which data blocks are carried by the GSMframe;

[0021]FIG. 5 is a block diagram illustrating the formation of down linktransmissions;

[0022]FIG. 6 is a block diagram illustrating the recovery of a datablock from a down link transmissions;

[0023]FIG. 7 is a flow chart illustrating operation of a wirelessterminal in receiving and processing a RF burst; and

[0024]FIG. 8 is a flow chart illustrating operations to recover a datablock according to an embodiment of the present invention;

[0025]FIGS. 9A and 9B are logic diagrams illustrating methods foroperating a wireless terminal to determine a BEP of a received burstaccording to the present invention;

[0026]FIG. 10 is a logic diagram illustrating another embodiment of amethod for operating a wireless terminal to determine a BEP of areceived burst according to the present invention;

[0027]FIG. 11 is a logic diagram illustrating an embodiment of thepresent invention in determining reported channel quality based upondecoding results;

[0028]FIG. 12 is a logic diagram illustrating an embodiment of thepresent invention in determining reported channel quality based upondecoding results;

[0029]FIG. 13 is a logic diagram illustrating an embodiment of thepresent invention that implements link adaptation decisions based on adownlink quality report; and

[0030]FIG. 14 is a logic diagram illustrating an embodiment of thepresent invention that implements link adaptation decisions based on adownlink quality report, wherein the link adaptation thresholds arealtered depending on the success of decoding the RF communications.

DETAILED DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a system diagram illustrating a portion of a cellularwireless communication system 100 that supports wireless terminalsoperating according to the present invention. The cellular wirelesscommunication system 100 includes a Mobile Switching Center (MSC) 101,Serving GPRS Support Node/Serving EDGE Support Node (SGSN/SESN) 102,base station controllers (BSCs) 152 and 154, link adaptation systems(LAS) 153, and base stations 103, 104, 105, and 106. The SGSN/SESN 102couples to the Internet 114 via a GPRS Gateway Support Node (GGSN) 112.A conventional voice terminal 121 couples to the PSTN 110. A Voice overInternet Protocol (VoIP) terminal 123 and a personal computer 125 coupleto the Internet 114. The MSC 101 couples to the Public SwitchedTelephone Network (PSTN) 110.

[0032] Each of the base stations 103-106 services a cell/set of sectorswithin which it supports wireless communications. Wireless links thatinclude both forward link components and reverse link components supportwireless communications between the base stations and their servicedwireless terminals. These wireless links support digital datacommunications, VoIP communications, and other digital multimediacommunications. The cellular wireless communication system 100 may alsobe backward compatible in supporting analog operations as well. Thecellular wireless communication system 100 supports the Global Systemfor Mobile telecommunications (GSM) standard and also the Enhanced Datarates for GSM (or Global) Evolution (EDGE) extension thereof. Thecellular wireless communication system 100 may also support the GSMGeneral Packet Radio Service (GPRS) extension to GSM. However, thepresent invention is also applicable to other standards as well, e.g.,TDMA standards, CDMA standards, etc. In general, the teachings of thepresent invention apply to digital communications that apply dynamiclink adaptation (LA) of the Modulation and Coding schemes (MCSs)utilized for communications between wireless terminals and servicingbase stations.

[0033] Wireless terminals 116, 118, 120, 122, 124, 126, 128, and 130couple to the cellular wireless communication system 100 via wirelesslinks with the base stations 103-106. As illustrated, wireless terminalsmay include cellular telephones 116 and 118, laptop computers 120 and122, desktop computers 124 and 126, and data terminals 128 and 130.However, the wireless system supports communications with other types ofwireless terminals as known to those skilled in the art as well. As isgenerally known, devices such as laptop computers 120 and 122, desktopcomputers 124 and 126, data terminals 128 and 130, and cellulartelephones 116 and 118, are enabled to “surf” the Internet 114, transmitand receive data communications such as email, transmit and receivefiles, and to perform other data operations. Many of these dataoperations have significant download data-rate (forward link)requirements while the upload data-rate (reverse link) requirements arenot as severe. Some or all of the wireless terminals 116-130 aretherefore enabled to support the EDGE operating standard. These wirelessterminals 116-130 also support the GSM standard and may support the GPRSstandard. Wireless terminals 116-130 support the LA decision makingprocess by determining the bit error probability (BEP) of received radiofrequency (RF) communications received from by base stations 103-106 andreporting this BEP to the wireless communication system 100. Linkadaptation systems (LAS) 153, shown operable coupled to BSC 152 and 154,use provided BEP and BLER information contained within a downlinkquality report to select an appropriate MCS (transmission scheme). Inmany cases, the BLER provides more objective data when compared to thatof the BEP. The BLER is an important indicator of link quality becausethe BLER may comprise or be derived from a bitmap that indicates whichsegments of the RF transmissions were requested to be retransmitted.Although LAS is shown operable coupled to the BSCs, the LAS may beoperable coupled to BSs 103-106.

[0034] Wireless terminals 116-130 support the pipelined processing ofreceived RF bursts in slots of a GSM frame so that a plurality of slotsin each sub-frame of a GSM frame are allocated for forward linktransmissions to a single wireless terminal. In one embodiment, a numberof slots of a GSM frame are allocated for forward link transmissions toa wireless terminal such that the wireless terminal must receive andprocess a number of RF bursts, e.g., 2, 3, 4, or more RF bursts, in eachGSM frame. The wireless terminal is able to process the RF burstscontained in these slots and still service reverse link transmissionsand the other processing requirements of the wireless terminal.

[0035]FIG. 2 is a block diagram functionally illustrating a wirelessterminal 200 constructed according to the present invention. Thewireless terminal 200 of FIG. 2 includes an RF transceiver 202, digitalprocessing components 204, and various other components contained withina housing. The digital processing components 204 includes two mainfunctional components, a physical layer processing, speech COder/DECoder(CODEC), and baseband CODEC functional block 206 and a protocolprocessing, man-machine interface functional block 208. A Digital SignalProcessor (DSP) is the major component of the physical layer processing,speech COder/DECoder (CODEC), and baseband CODEC functional block 206while a microprocessor, e.g., Reduced Instruction Set Computing (RISC)processor, is the major component of the protocol processing,man-machine interface functional block 208. The DSP may also be referredto as a Radio Interface Processor (RIP) while the RISC processor may bereferred to as a system processor. However, these naming conventions arenot to be taken as limiting the functions of these components.

[0036] The RF transceiver 202 couples to an antenna 203, to the digitalprocessing components 204, and also to a battery 224 that powers allcomponents of the wireless terminal 200. The physical layer processing,speech COder/DECoder (CODEC), and baseband CODEC functional block 206couples to the protocol processing, man-machine interface functionalblock 208 and to a coupled microphone 226 and speaker 228. The protocolprocessing, man-machine interface functional block 208 couples to aPersonal Computing/Data Terminal Equipment interface 210, a keypad 212,a Subscriber Identification Module (SIM) port 213, a camera 214, a flashRAM 216, an SRAM 218, a LCD 220, and LED(s) 222. The camera 214 and LCD220 may support either/both still pictures and moving pictures. Thus,the wireless terminal 200 of FIG. 2 supports video services as well asaudio services via the cellular network.

[0037]FIG. 3 is a block diagram illustrating in more detail the wirelessterminal of FIG. 2, with particular emphasis on the digital processingcomponents of the wireless terminal. The digital processing components204 include a system processor 302, a baseband processor 304, and aplurality of supporting components. The supporting components include anexternal memory interface 306, MMI drivers and I/F 308, a video I/F 310,an audio I/F 312, a voice band CODEC 314, auxiliary functions 316, amodulator/demodulator 322, ROM 324, RAM 326 and a plurality ofprocessing modules. In some embodiments, the modulator/demodulator 322is not a separate structural component with these functions beingperformed internal to the baseband processor 304.

[0038] The processing modules are also referred to herein asaccelerators, co-processors, processing modules, or otherwise, andinclude auxiliary functions 316, an equalizer module 318, anenCOder/DECoder (CODEC) processing module 320, and an IncrementalRedundancy (IR) processing module 328. The interconnections of FIG. 3are one example of a manner in which these components may beinterconnected. Other embodiments support additional/alternatecouplings. Such coupling may be direct, indirect, and/or may be via oneor more intermediary components.

[0039] RAM and ROM service both the system processor 302 and thebaseband processor 304. Both the system processor 302 and the basebandprocessor 304 may couple to shared RAM 326 and ROM 324, couple toseparate RAM, coupled to separate ROM, couple to multiple RAM blocks,some shared, some not shared, or may be served in a differing manner bythe memory. In one particular embodiment, the system processor 302 andthe baseband processor 304 coupled to respective separate RAMs and ROMsand also couple to a shared RAM that services control and data transfersbetween the devices. The processing modules 316, 318, 320, 322, and 328may coupled as illustrated in FIG. 3 but may also coupled in othermanners in differing embodiments.

[0040] The system processor 302 services at least a portion of aserviced protocol stack, e.g., GSM/GPRS/EDGE protocol stack. Inparticular the system processor 302 services Layer 1 (L1) operations330, a portion of Incremental Redundancy (IR) GSM protocol stackoperations 332 (referred to as “IR control process”), Medium AccessControl (MAC) operations 334, and Radio Link Control (RLC) operations336. The baseband processor 304 in combination with themodulator/demodulator 322, RF transceiver, equalizer module 318, and/orencoder/decoder module 320 service the Physical Layer (PHY) operationsperformed by the digital processing components 204. The basebandprocessor 304 may also services a portion of the GSM/GPRS/EDGE protocolstack.

[0041] Still referring to FIG. 3, the baseband processor 304 controlsthe interaction of the baseband processor 304 and equalizer module 318.As will be described further with reference to FIGS. 5-6B, the basebandprocessor 304 is responsible for causing the equalizer module 318 andthe CODEC processing module 320 to process received RF bursts thatreside within slots of a GSM frame. In the particular embodiment ofFIGS. 2 and 3, with single RF front end 202, wireless terminal 200 mayreceive and process RF bursts in up to four slots of each GSM frame,i.e., be assigned four slots for forward link transmissions in anyparticular GSM frame. In another embodiment in which the wirelessterminal 200 includes more than one RF front end, the wireless terminal200 may be assigned more than four slots in each sub-frame of the GSMframe. In this case, required transmit operations would be performedusing a second RF front end while a first RF front end would perform thereceive operations. When the forward link transmissions and the reverselink transmissions occupy different channels with sufficient frequencyseparation, and the wireless terminal otherwise supports full duplexoperations, the wireless terminal could receive and transmit at the sametime.

[0042] The combination of the RF front end 202, and base band processor204, which may include an optional CODEC processing module, receive RFcommunications from the servicing base station. In one embodiment the RFfront end 202 and base band processor 204 receive and process RF burstsfrom servicing base stations. The combination of RF front end 202 andbase band processor 204 are operable to receive RF bursts transmittedaccording to a transmission scheme wherein the transmission schemeincludes both a modulation format and a coding format. Base bandprocessor 204 to produce a data block decodes sequences of softdecisions, extracted from the RF bursts. The sequence of soft decisionsmay decode successfully into the data block as indicated by errorcorrection coding results. These soft decisions may be protected bycyclical redundant coding (CRC) such as fire coding and convolutionalcoding. The combination determines whether the decoding of the datablock was successful and uses this information to help determined thereported BEP for the data block. When the decoding is unsuccessful thereported BEP is set to the measured BEP plus an increment step size orshould the decoding be successful, the reported BEP is set to themeasured BEP minus a decrement step size. The reported BEP may be set toa BEP threshold when the decoding is unsuccessful and the BEP thresholdexceeds the measured BEP.

[0043] Re-encoding of properly decoded data blocks produces a sequenceof re-encoded decisions which when compared to the sequence of softdecisions produces a Re-encoded Bit Error (RBER). The BEP reported tothe servicing base station is based upon the estimated BEP derived fromthe SNR and the RBER. When the decoding is unsuccessful, the BEP may bebased upon more heavily or solely the estimated BEP provided by the SNR.Similarly, when the decoding is successful, the BEP may be based uponmore heavily or solely the RBER or BLER. The BLER is often considered asgiving a more objective quality measurement than the BEP or RBER. Thisallows the BEP to more accurately reflect actual channel conditions.Thus, LA decisions can more effectively select an appropriate MCS basedupon existing channel conditions.

[0044]FIG. 4 is a block diagram illustrating the general structure of aGSM frame and the manner in which data blocks are carried by the GSMframe. The GSM frame is 4.615 ms in duration, including guard periods,and each of which includes eight slots, slots 0 through 7. Each slot isapproximately 577 μs in duration, includes a left side, a midamble, anda right side. The left side and right side of a normal RF burst of thetime slot carry data while the midamble is a training sequence.

[0045] The RF bursts of four time slots of the GPRS block carry asegmented RLC block, a complete RLC block, or two RLC blocks, dependingupon a supported Modulation and Coding Scheme (MCS) mode. For example,data block A is carried in slot 0 of sub-frame 1, slot 0 of sub-frame 2,slot 0 of sub-frame 3, and slot 0 of sub-frame 3. Data block A may carrya segmented RLC block, an RLC block, or two RLC blocks. Likewise, datablock B is carried in slot 1 of sub-frame 1, slot 1 of sub-frame 2, slot1 of sub-frame 3, and slot 1 of sub-frame 3. The MCS mode or CS mode ofeach set of slots, i.e., slot n of each sub-frame, for the GSM frame isconsistent for the GSM frame. Further, the MCS mode or CS mode ofdiffering sets of slots of the GSM frame, e.g., slot 0 of each sub-framevs. any of slots 1-7 of each sub-frame, may differ. This ability allowsLA to be implemented. As will be described further with reference toFIG. 5, the wireless terminal 200 may be assigned multiple slots forforward link transmissions that must be received and processed by thewireless terminal 200.

[0046]FIG. 5 depicts the various stages associated with mapping datainto RF bursts. A Data Block Header and Data are initially unencoded.The block coding operations perform the outer coding for the data blockand support error detection/correction for data block. The outer codingoperations typically employ a cyclic redundancy check (CRC) or a FireCode. The outer coding operations are illustrated to add tail bitsand/or a Block Code Sequence (BCS), which is/are appended to the Data.After block coding has supplemented the Data with redundancy bits forerror detection, calculation of additional redundancy for errorcorrection to correct the transmissions caused by the radio channels.The internal error correction or coding scheme of GSM is based onconvolutional codes.

[0047] Some redundant bits generated by the convolutional encoder arepunctured prior to transmission. Puncturing increases the rate of theconvolutional code and reduces the redundancy per data blocktransmitted. Puncturing additionally lowers the bandwidth requirementssuch that the convolutional encoded signal fits into the availablechannel bit stream. The convolutional encoded punctured bits are passedto an interleaver, which shuffles various bit streams and segments theinterleaved bit streams into the 4 bursts shown.

[0048] Each RF burst has a left side, a midamble, and a right side. Theleft side and right side contain data. The midamble consists ofpredefined, known bit patterns, the training sequences, which are usedfor channel estimation to optimize reception with an equalizer and forsynchronization. With the help of these training sequences, theequalizer eliminates or reduces the intersymbol interferences, which canbe caused by propagation time differences of multipath propagation. Anumber of training sequences are defined for normal RF bursts in the GSMstandard. However, the exact configuration of the training sequences maydepend on the modulation format used. Each set of four bursts typicallyutilizes the same modulation format. By analyzing the training sequenceone can determine the modulation format.

[0049]FIG. 6 is a block diagram depicting the various stages associatedwith recovering a data block from RF bursts. Four RF bursts making up adata block are received and processed. Once all four RF bursts have beenreceived, the RF bursts are combined to form an encoded data block.However, in some instances the encoded data block may be recovered fromfewer than all four RF bursts. This ability depends upon the robustnessof the modulation format and coding scheme. The encoded data block isthen depunctured (if required), decoded according to an inner decodingscheme, and then decoded according to an outer decoding scheme. Thedecoded data block includes the data block header and the data.Successful decoding may be signaled by appropriate tailbits appended tothe data following convolutional decoding (error correction coding).

[0050]FIG. 7 is a flow charts illustrating operation of a wirelessterminal 200 in receiving and processing RF bursts. The operationsillustrated correspond to a single RF burst in a corresponding slot ofGSM frame. The RF front end 202, the baseband processor 304, and theequalizer module 318 illustrated in FIG. 3 perform these operations.These operations are generally called out as being performed by one ofthese components. However, the split of processing duties among thesevarious components may differ without departing from the scope of thepresent invention.

[0051] A single processing device or a plurality of processing devicesoperably coupled to memory performs the processing duties. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory may be a single memory device or a plurality ofmemory devices. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. Note that when the processing duties areimplemented via a state machine, analog circuitry, digital circuitry,and/or logic circuitry, the memory storing the corresponding operationalinstructions may be embedded within, or external to, the circuitrycomprising the state machine, analog circuitry, digital circuitry,and/or logic circuitry. The processing duties include the execution ofoperational instructions corresponding to at least some of the stepsand/or functions illustrated in FIGS. 6-10.

[0052] Referring particularly to FIG. 7, operation commences with the RFfront end 202 receiving an RF burst in a corresponding slot of a GSMframe (step 602). The RF front end 202 then converts the RF burst to abaseband signal (step 604). Upon completion of the conversion, the RFfront end 202 stores the converted baseband signal. When needed thebaseband processor samples the converted baseband signal from the RFfront end. Thus, as referred to in FIG. 7, the RF front end 202 performssteps 602-604.

[0053] Operation continues with the baseband processor 304 receiving thebaseband signal (step 608). In a typical operation, the RF front end202, the baseband processor 304, or modulator/demodulator 322 samplesthe analog baseband signal to digitize the baseband signal. Afterreceipt of the baseband signal (in a digitized format), the basebandprocessor 304 performs blind detection of a modulation format of thebaseband signal (step 610). This blind detection of the modulationformat determines the modulation format of the corresponding basebandsignal. Proper determination of the modulation format is necessary inorder to properly determine the SNR of the channel and RBER associatedwith the data contained within the RF bursts. In one particularembodiment according to the GSM standard, the modulation format will beeither Gaussian Minimum Shift Keying (GMSK) modulation or Eight PhaseShift Keying (8PSK) modulation. The baseband processor 304 makes thedetermination (step 612) and appropriately processes the RF bursts basedupon the detected modulation format.

[0054] The baseband processor performs pre-equalization processing ofthe RF bursts in step 612. For GMSK modulation, this processing involvesde-rotation and frequency correction; burst power estimation; timing,channel, noise, and signal-to-noise ratio (SNR) estimation; automaticgain control (AGC) loop calculations; soft decision scaling factordetermination; and matched filtering operations on the baseband signal.For 8PSK modulation, pre-equalization processing of the RF burstsinvolves de-rotation and frequency correction; burst power estimation;timing, channel, noise, and SNR estimations; AGC loop calculations;Decision Feedback Equalizer (DFE) coefficients calculations; and softdecision scaling factors for the baseband signal. The SNR estimationfrom the pre-equalization processing operations may be used later todetermine the estimated BEP. Determination of the estimated BEP will bediscussed further in FIGS. 9-11. These pre-equalization processingoperations produce a processed baseband signal. Upon completion of thesepre-equalization processing operations, the baseband processor 304issues a command to the equalizer module 318.

[0055] The equalizer module 318, upon receiving the command, prepares toequalize the processed baseband signal based upon the modulation format,e.g., GMSK modulation or 8PSK modulation in step 614. The equalizermodule 318 receives the processed baseband signal, settings, and/orparameters from the baseband processor 304 and equalizes the processedbaseband signal. For GMSK, equalization-processing operations involveMaximum Likelihood Sequence Estimation (MLSE) equalization on the leftside and right side of the baseband signal to produce soft decisions forthe left side and right side. As was shown previously with reference toFIG. 4, each RF burst contains a left side of data, a midamble, and aright side of data. The midamble includes predefined training sequencethat may be based on the modulation format. For 8PSK, the equalizermodule 318 first prepares state values that it will use in equalizingthe 8PSK modulated processed baseband signal. Then equalizer module 318uses a Maximum A posteriori Probability (MAP) equalizer to equalize theleft and right sides of the processed baseband signal to produce softdecisions for the processed baseband signal.

[0056] After equalization, the equalizer module 318 then issues aninterrupt to the baseband processor 304 indicating that the equalizeroperations are complete for the RF bursts. The baseband processor 304then receives the soft decisions from the equalizer module 318. Next,the baseband processor 304 performs “post-equalization processing” asshown in step 616. This may involve determining an average phase of theleft and right sides based upon the soft decisions received from theequalizer module 318 and frequency estimation and tracking based uponthe soft decisions received from the equalizer module 318.

[0057] The sequences of soft decisions are decoded in step 618. Oneparticular method of decoding the soft decisions is further detailed inFIG. 8. The decoded soft decisions may be used to produce a RBER. Thisprocess of producing an RBER will be described in further detail inassociation with the description of FIGS. 9-11 and following. With theestimated BEP and/or RBER, baseband processor 304 or system processor302 produce a BEP, which is reported to the servicing base station.While the operations of FIG. 7 are indicated to be performed byparticular components of the wireless terminal, such segmentation ofoperations could be performed by differing components. For example, thebaseband processor 304 or system processor 302 in other embodimentscould perform the equalization operations. Further, the basebandprocessor 304 or the system processor 302 in other embodiments couldalso perform decoding operations.

[0058]FIG. 8 is a flow chart illustrating operations to decode a datablock according to an embodiment of the present invention. Operationscommence with receiving and processing an RF burst in step 702 and asdescribed with reference to FIG. 7. After receiving the four RF burststhat complete an EDGE or GPRS data block, as determined at step 704,operation proceeds to step 706.

[0059] A header of the data block identifies the coding scheme andpuncturing pattern of the data block. For example, the coding scheme maybe any one of the MCS-1 through MCS-9 coding schemes, each of which mayinclude multiple puncturing patterns. Operation according to the presentinvention uses the training sequence of each RF burst, located withinthe midamble of the RF burst, to identify the modulation format of theRF bursts.

[0060] Data recovery begins in step 706 where, if necessary, the datablock is decrypted. The data block is then de-interleaved (step 708)according to a particular format of the data block, e.g. MCS-1 throughMCS-9. The data block is then de-punctured (step 710). At step 712, thede-interleaved and de-punctured data block is decoded. Decodingoperations may include combining previously received copies of the datablock with the current copy of the data block. Data bits of the decodeddata block are then extracted and processed further (step 714). Properlydecoded data blocks can be re-encoded to produce a sequence ofre-encoded decisions that when compared to the sequence of softdecisions result in the RBER. The RBER may provide a more accurateindication of the performance of the selected MCS than that provided bythe estimated BEP, which is based on the SNR.

[0061]FIG. 9A is a logic diagram illustrating a method for operating awireless terminal to determine a BEP of a received bursts according tothe present invention. The method commences with receiving the RF burstsin step 902. Next, the signal-to-noise (SNR) of the RF bursts isdetermined in step 904. The determination of the SNR in step 904 istypically completed as part of the pre-equalization processing of step612. One embodiments utilizes the extracted training sequences of the RFbursts to produce the SNR and map to an estimated BEP based on the MCS.Continuing with step 906, a sequence of soft decisions is extracted fromthe payload. This sequence may correspond to the training sequence ordata, wherein the greater number of samples available within the dataportion would yield more accurate results than those derived from thesmaller sample set of the training sequence. An attempt to decode thesequence of soft decisions is made in step 908. When the attempt todecode the plurality of soft decisions is unsuccessful (as determined atdecision point 910), the BEP of the RF bursts is determined based uponthe SNR (estimated BEP) in step 912. When the sequence of soft decisionsdecodes successful at decision point 910, the data bits are re-encodedto produce a sequence re-encoded decisions at step 914. Then, thesequence of re-encoded decisions is compared to the sequence ofsoft-decisions in step 916. This comparison results in a RBER upon whichthe BEP may be based (step 918). The BEP may be transmitted to aservicing base station in step 920. This process may also include thehistorical performance of the BEP in determining the BEP reported to theservicing base station by including the mean and/or standard deviationin the determination of the BEP. This reported BEP may be included in adownlink quality level reported by the wireless terminal to theservicing base station.

[0062] Another embodiment, as illustrated in FIG. 9B, determines theestimated BEP in step 905 with the SNR value of step 904. Additionally,this embodiment assigns a threshold value to the RBER at step 911 whenthe attempt to decode the plurality of soft decisions is unsuccessful(as determined at decision point 910). This allows the BEP of the RFbursts to be determined based upon both the SNR (estimated BEP of step905) and RBER when unsuccessful decoding occurs. This combination mayreduce the BEP reported to the servicing base station when a BEP basedonly on SNR would prove overly optimistic. Similarly, when the sequenceof soft decisions decodes successfully at decision point 910, the BEP ofthe RF bursts may be determined based upon both the SNR (estimated BEPof step 905) and RBER the data bits, wherein different weighting valuesor coefficients are assigned to the SNR and RBER. These weighting valuesor coefficients may be based on whether or not the sequence of softdecisions decodes successfully. For example, the weighting values mayweigh the SNR more heavily when the sequence of soft decisions decodesunsuccessfully. Alternatively, the weighting values may weigh the RBERmore heavily when the sequence of soft decisions decodes successfully.Further, a comparison between the SNR and assigned threshold value ofthe RBER when the sequence of soft decisions decodes unsuccessfully mayexamine the relative magnitude of the estimated BEP and RBER and selectthe BEP to be the greater of the two. As in FIG. 9A, this process mayalso include the historical performance of the BEP in determining theBEP reported to the servicing base station within the downlink qualityreport by including the mean and/or standard deviation, or other likefunctions, in the determination of the BEP. In yet another embodiment tobe described in FIG. 11, the BEP reported to the servicing base stationmay be incremented or decremented depending on whether or not thesequence of soft decisions decodes successfully.

[0063]FIG. 10 is a logic diagram illustrating another embodiment of amethod for operating a wireless terminal to determine a BEP of receivedRF bursts according to the present invention. As previously stated, Linkadaptation (LA) provides a mechanism used in EDGE to adapt the channelcoding schemes and modulation formats to the changing radio linkconditions. LA allows the network to command the handset to change tothe different modulation and coding scheme that is best for the currentradio condition. To facilitate the network to do so, the handset reportsa downlink quality report to the network via the servicing base station.The downlink quality report may include an estimated BEP based on theSNR of the RF bursts and the RBER of the RF bursts as well as the meanBEP (Mean_BEP) and standard deviation of the BEP (CV_BEP) of a RLC block(4 radio bursts) averaged over the reporting period and all assignedtime slots per modulation type. They are derived as follows:$\begin{matrix}{{MEAN\_ BEP}_{n} = \frac{\sum\limits_{j}^{\quad}\quad {{R_{n}^{(j)} \cdot {MEAN\_ BEP}}{\_ TN}_{n}^{(j)}}}{\sum\limits_{j}^{\quad}\quad R_{n}^{(j)}}} \\{{CV\_ BEP}_{n} = \frac{\sum\limits_{j}^{\quad}\quad {{R_{n}^{(j)} \cdot {CV\_ BEP}}{\_ TN}_{n}^{(j)}}}{\sum\limits_{j}^{\quad}\quad R_{n}^{(j)}}}\end{matrix}$

[0064] Where

[0065] n=the iteration index at reporting time

[0066] j=the channel number.

[0067] And

R _(n)=(1−e)·R _(n−1) +e·x _(n) , R ⁻¹=0 $\begin{matrix}\begin{matrix}{{{MEAN\_ BEP}{\_ TN}_{n}} = {{{\left( {1 - {e \cdot \frac{x_{n}}{R_{n}}}} \right) \cdot {MEAN\_ BEP}}{\_ TN}_{n - 1}} +}} \\{\quad {e \cdot \frac{x_{n}}{R_{n}} \cdot {MEAN\_ BEP}_{{block},n}}} \\{{{CV\_ BEP}{\_ TN}_{n}} = {{{\left( {1 - {e \cdot \frac{x_{n}}{R_{n}}}} \right) \cdot {CV\_ BEP}}{\_ TN}_{n - 1}} + {e \cdot \frac{x_{n}}{R_{n}} \cdot}}} \\{\quad {CV\_ BEP}_{{block},n}}\end{matrix} & \left( {{Eq}.\quad 1} \right)\end{matrix}$

[0068] Where:

[0069] n is the iteration index, incremented per downlink radio block.

[0070] R_(n) denotes the reliability of the filtered quality parameters.

[0071] e is the forgetting factor defined by the network.

[0072] x_(n) denotes the existence of quality parameters for the n^(th)block, i.e. whether the radio block is intended for this MS. x_(n)values 1 or 0, denoting the existence and absence of quality parameters,respectively.

[0073] Key challenges in LA are the algorithm used in the network forlink adaptation control, and the accuracy of the MEAN_BEP_(block, n) andCV_BEP_(block, n) calculated by the handset, where MEAN_BEP_(block, n)is the BEP value averaged over at least one given RLC block andCV_BEP_(block, n) is the corresponding standard deviation.

[0074] There are several ways to obtain MEAN_BEP_(block, n). Forexample, the MEAN_BEP_(block, n) can be derived based on: (1)signal-to-noise ratio (SNR); (2) re-encoding correctly decoded data; or(3) the training sequence. SNR-based BEP requires robust SNR-to-BEPmapping table that covers all types of propagation environments. SNRbased approximations often overestimate system performance. This overestimation of system performance can result in optimistic BEPs beingused to make LA decisions. LA decisions based upon optimistic BEP canresult in lost communications between the wireless terminal and theservicing base station. Furthermore, extensive computer simulations aretherefore needed to generate this mapping table.

[0075] RBER count provides a better measurement for the current linkquality regardless of the radio propagation environments. Thusre-encoding based BEP can better reflect the link quality, however, thisvalue is available only if the data block is decoded correctly. Trainingsequence based BEP calculation can be easily obtained but it does notprovide enough samples (26 for GMSK, 78 for 8PSK) for BEP averaging.However, one bad RBER count could severely impact the selected MCS.Therefore historical factors such as the mean and standard deviationprovide improved ways of establishing thresholds for LA decisions. Thepresent invention provides better results by combining methods 1 through3.

[0076] One particular embodiment uses a joint SNR and re-encoding basedBEP algorithm. This allows the wireless terminal to report the BEPregardless of the data decoding status. The estimated RF bursts SNR maybe derived using the training sequence. The estimated RF bursts SNR andcorresponding modulation type, determined as described in FIG. 7, arethen placed in shared memory for the ARM to process the final BEPreport. SNR-BEP tables, derived from AWGN channel for 8PSK and GMSKtogether with pre-defined thresholds, and RBER, constitute the basis ofthis algorithm. The pre-defined threshold is denoted as BEP_th. Thisthreshold depends on the MCS mode and is determined by theerror-correction capability of the given MCS mode.

[0077] Referring now to the operations of FIG. 10, a burst is received(step 1002). The burst will typically be one of four portions of an RLCblock and typically carries a training sequence (mid amble), a header, adata block, and a tail/trailer. Upon receipt of the RF burst, an attemptis made to decode the header (step 1004). Decoding the header allows thecoding scheme to be readily identified. This information is coupled withknowledge to the modulation format to determine the MCS of the RFbursts. If the decode is not successful (as determined at step 1006), noBEP update is performed (step 1008) and operation returns to step 1002wherein another burst is awaited. If the header decode is successful (asdetermined at step 1006), operation proceeds to step 1010 where thewireless terminal determines whether the data block carried in thebursts is intended for the wireless terminal. If the data block is notintended for the wireless terminal, the operation proceeds to step 1008and no BEP update/calculation occurs. This prevents unnecessary BEPcalculations and potential LA decisions being based on communicationsnot intended for the wireless terminal.

[0078] If the data block carried in the bursts does belong to thewireless terminal (as determined at step 1010), the wireless terminalnext determines whether the Block Sequence Number (BSN) of the datablock is within a receiving window under consideration (step 1012). Ifnot, the BEP is updated based upon the SNR of the block (at step 1014)and operation proceeds from step 1014 to step 1002 where another burstis awaited. If the BSN is inside the receiving window (as determined atstep 1012) it is next determined whether Incremental Redundancy (IR) isto be performed upon the received block (step 1016). If IR is to beperformed, operation proceeds to step 1014. If not, the wirelessterminal attempts to decode the received data block (step 1018).

[0079] If the decode attempt of step 1020 is successful, as determinedat step 1020, the decoded data is re-encoded in step 1022 to produce aRBER based upon the re-encoded data, and the BEP is updated based uponthe RBER count in step 1024. If the decoding attempt is not successful(as determined at step 1020), operation proceeds to step 1026 where theBEP is updated based upon the maximum of the estimated BEP based on SNR,or BEP(mean_SNR), and the pre-defined threshold, BEP_th. From both steps1024 and 1026 operation returns to step 1002. The BEP update may furtherinclude the historical performance of the BEP in determining the BEPupdate to the servicing base station by including the mean and/orstandard deviation of the BEP update in the determination of the BEP.

[0080] In the operation of FIG. 10, therefore, SNR is typicallycalculated with the training sequence of the bursts to map to anestimated BEP and will be used for BEP calculation whenever the RBER isnot available. The training sequence may also be used to produce an RBERbased on a smaller sample set than using the data portion would provide.Generally, the SNR provides a reasonable link quality measure forchannels free of inter-symbol interference. For channel withinter-symbol interference, SNR alone is not sufficient to measure thequality of the link. Instead, RBER count is a better quality measure.When data decoding fails, the RBER cannot be obtained. In this case,SNR-based BEP calculation will be used with the additional fact thatdata decoding has failed. This information can help better quantify thedownlink quality in combination with the SNR. When data decoding fails,the number of errors in the received block has to exceed some threshold.Therefore, the RBER can be assumed to reach this threshold. Thisthreshold, for a given MCS mode, is related to the error correctioncapability of the mode and can be obtained via measurements orsimulations. The threshold needs to be carefully selected and tested.

[0081]FIG. 11 is a logic diagram illustrating an embodiment of thepresent invention in determining reported downlink channel quality basedupon decoding results. FIG. 11 illustrates an adaptive channel qualityestimation algorithm within the context of an EDGE system (Enhanced Datarate for GSM Evolution). However, the teachings illustrated in FIG. 11may be applied to other systems equally well. In an EDGE system,MEAN_BEP_(block,n) is defined as the BEP value averaged over 4 radiobursts for a given RLC block and CV_BEP_(block,n) is the correspondingstandard deviation. There are several ways to obtain MEAN_BEP_(block,n)in EDGE system. It can be derived based on the (1) signal-to-noise ratio(SNR), (2) re-encoding correctly decoded data, and (3) using trainingsequence.

[0082] Whether the LA can be effective highly depends on the accuracy ofthe channel downlink quality reports from the wireless terminal and theLA threshold adjustment from the network. However, measurement errorsare unavoidable from wireless terminals that experience a fast changingwireless condition. Moreover, the LA threshold on the network is usuallyadjusted based upon one (or a very few) available test wirelessterminals. As a result, these thresholds may not be appropriate forother wireless terminals, leading to unsuitable transmission formatsbeing used for the wireless terminal and thus lower the data throughput.In the worst case, this will lead to data transfer stall, which is moreprominent in low receive signal strength conditions (RSSI). To addressthis issue, the operations of FIG. 11 illustrate an adaptive channelquality estimation algorithm for the wireless communication systems thatemploy link adaptation. BEP is used in FIG. 11 as an example of thechannel quality measures to describe the adaptive channel qualityestimation algorithm.

[0083] Operation commences in obtaining the downlink channel qualitymeasurements (e.g. MEAN_BEP and CV_BEP) using any available algorithm(step 1102). Next, an RLC block is received (step 1104), decoding isattempted (step 1106), and it is determined whether the decoding attemptwas successful at decision point 1108.

[0084] For each RLC block with a decoding error, two steps need to beperformed. In a first step 1110, MEAN_BEP_(n)=max(MEAN_BEP_(n,measure),MEAN_BEP_(threshold)), where MEAN_BEP_(n,measure) is the measuredMEAN_BEP for block n, and MEAN_BEP_(threshold) is the BEP threshold forthe given transmission format, which is determined by its errorcorrection capability. Further the MEAN_BEP_(threshold) is increasedaccordingly for each such decoding error, by settingMEAN_BEP_(threshold)(new)=MEAN_BEP_(threshold)(old)+Step_size(up) (step1112). In such case, Step_size(up) (>=0) is the increment of MEAN_BEPthreshold. This value can be obtained via simulation or experiment.

[0085] For each RLC block that is decoded successfully, two steps needto be performed. In a first step 1114, setMEAN_BEP_(n)=MEAN_BEP_(n,measure). In a second step, theMEAN_BEP_(threshold) is set accordingly for each success by settingMEAN_BEP_(threshold)(new)=MEAN_BEP_(threshold)(old)−Step_size(down)(step 1116). At step 1116, Step_size(down) (>=0) is the decrement ofMEAN_BEP threshold. Again this value can be obtained via simulation orexperiment and it is usually smaller than Step_size(up) to maintain thestability of the system. From each of steps 1112 and 1116 operationreturns to step 1102.

[0086] The advantage of the operations illustrated in FIG. 11 is thatthe reported channel quality (e.g. MEAN_BEP) is directly related to thehistorical decoding success rate on the downlink, which is normallyrepresented by block error rate (BLER). As a result, if the wirelessterminal experiences more decoding errors on the downlink, thecorresponding channel quality will be adjusted downward, whichfacilitates the network to use more robust transmission format. Thissignificantly reduces the transmission problem due to measurement errorsor un-matching link adaptation thresholds. This feature is especiallyuseful when the wireless terminal operates in low RSSI conditions orexperiences some unpredictable fading conditions.

[0087]FIG. 12 is a logic diagram illustrating a method for operating awireless terminal to determine a reported BEP within a downlink qualityreport associated with a received burst. The method commences withreceiving the RF burst in step 1202. Continuing with step 1204, asequence of soft decisions is extracted from the RF bursts. Thissequence may correspond to the training sequence or data, wherein thegreater number of samples available within the data portion would yieldmore accurate results than those derived from the smaller sample set ofthe training sequence. An attempt to decode the sequence of softdecisions is made at step 1206. When the attempt to decode the pluralityof soft decisions is unsuccessful (as determined at decision point1208), the measured BEP may be determined based upon the SNR (estimatedBEP) as described in step 912 of FIG. 9A, based upon the SNR (estimatedBEP) and RBER as described in step 918 of FIG. 9B, or based upon themaximum of the estimated BEP based on SNR and the pre-defined thresholdas described in step 1026 of FIG. 10. The measured BEP may furtherinclude the historical performance of the measured BEP by including themean and/or standard deviation of the measured BEP. Then the measuredBEP as determined in step 1210 is incremented by an increment step sizein step 1212 to yield a reported BEP value, which is transmitted to theservicing base station in step 1218.

[0088] Returning to decision point 1208, when the attempt to decode theplurality of soft decisions is successful the measured BEP may bedetermined based upon the RBER only as described in steps 914 through918 of FIG. 9A and step 1024 of FIG. 10, or the RBER and SNR (estimatedBEP) as described in step 914 through 819 of FIG. 9B. The measured BEPmay further include the historical performance of the measured BEP byincluding the mean and/or standard deviation of the measured BEP. Thenthe measured BEP as determined in step 1214 is decremented by adecrement step size in step 1216 to yield a reported BEP value, which isthen transmitted to the servicing base station in step 1218. FIG. 13 isa logic diagram illustrating the implementation of LA decision within awireless communication system, such as a cellular network. The methodcommences in step 1302 with the implementation of an initialtransmission scheme (MCS) between the wireless terminals and servicingbase stations. Continuing with step 1304, a downlink quality report isgenerated by the wireless terminals and provided to the servicing basestation. This downlink quality report is based on the reported BEP.Various methods exist for determining the reported BEP, including thosedescribed with FIGS. 9A, 9B, 10, 11, and 12. If the downlink qualityreport compares favorably to the link adaptation thresholds, the currenttransmission scheme is maintained in Step 1312. Monitoring of thedownlink quality report then continues in step 1322. The LA thresholdsestablish quality levels when it becomes necessary to change thetransmission scheme. Other additional criteria may be used to change thetransmission scheme that relate to network loading, call priority orother factors known to those skilled in the art. The monitored downlinkquality report is then compared to the LA thresholds for individualwireless terminals as the process returns to step 1308. Typically one LAthreshold has been used for all the wireless terminals. Not only doesthis embodiment allow for adjusting LA thresholds, individual LAthresholds associated with individual wireless terminals may beindependently adjusted. This adjustment may be downwards when thecomparison between the downlink quality report and the LA thresholds isunfavorable. Additionally, when the comparison is unfavorable, the linkadaptation system may attempt to identify an alternative transmissionscheme that is expected to yield an improved downlink quality report instep 1314. This improved downlink quality report corresponds to animproved quality of the communications experienced by the end users. Ifan alternate transmission scheme is identified at decision point 1316,then the alternate transmission scheme is implemented at Step 1318.Monitoring of future downlink quality reports continues in Step 1322.However, if an alternate transmission scheme is not identified atdecision point 1316, it is necessary to maintain the currenttransmission scheme at step 1320. Again, monitoring of the downlinkquality report continues at Step 1322 with the process returning to step1308.

[0089]FIG. 14 is a logic diagram illustrating another method for makingand implementing link adaptation decisions within a wirelesscommunication system. This implementation allows the LA thresholds to beadjusted for individual wireless terminals. At step 1402, an initialtransmission scheme is implemented between wireless terminals andservicing base stations. The wireless terminals generate downlinkquality reports at step 1404, which in turn are provided to theservicing base station's and their operable coupled link adaptationsystems in step 1406. This downlink quality report is compared to the LAthresholds in step 1408. When the downlink quality report comparesfavorably to the link adaptation threshold at decision point 1410, thecurrent transmission scheme is maintained and the processes is directedto step 1412. However, if the downlink quality report comparesunfavorably with the link adaptation threshold at decision point 1410,an alternative transmission scheme is identified at step 1414 whereinthe alternative transmission scheme is expected to yield an improveddownlink quality report. If such an alternative transmission scheme isidentified, the alternative transmission scheme is then implemented instep 1416. The process continues to monitor the downlink quality reportin step 1418 whether the current transmission scheme was maintained oran alternate transmission scheme was implemented as directed from step1412 or step 1416, respectively. Further, a determination is made as towhether the data from the RF communications decoded successfully in step1420. If the communications decoded successfully as determined indecision point 1422, the link adaptation threshold may be decremented bya decrement step size in step 1424 for future comparisons as the processcontinues to step 1408. Otherwise, the link adaptation thresholds may beincremented by an increment step size at step 1426 for use in futurecomparisons within Step 1408. By incrementing or decrementing the linkadaptation thresholds, the possibility of spurious LA decisions may bereduced to avoid unnecessary LA changes. This helps maintain asuccessful communication transmission scheme when the communications aredecoding properly. Similarly if the data is decoding improperly,incrementing the LA thresholds helps to force an unfavorable comparisonbetween the downlink quality report and the link adaptation threshold.This unfavorable comparison at decision point 1410 is necessary toidentify and implement an alternative transmission scheme as describedin steps 1414 and 1416.

[0090] As one of average skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term. Such anindustry-accepted tolerance ranges from less than one percent to twentypercent and corresponds to, but is not limited to, component values,integrated circuit process variations, temperature variations, rise andfall times, and/or thermal noise. As one of average skill in the artwill further appreciate, the term “operably coupled”, as may be usedherein, includes direct coupling and indirect coupling via anothercomponent, element, circuit, or module where, for indirect coupling, theintervening component, element, circuit, or module does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As one of average skill in the art will alsoappreciate, inferred coupling (i.e., where one element is coupled toanother element by inference) includes direct and indirect couplingbetween two elements in the same manner as “operably coupled”. As one ofaverage skill in the art will further appreciate, the term “comparesfavorably”, as may be used herein, indicates that a comparison betweentwo or more elements, items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1.

[0091] The foregoing description of a preferred embodiment of theinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed, and modifications andvariations are possible in light of the above teachings or may beacquired from practice of the invention. The embodiment was chosen anddescribed in order to explain the principles of the invention and itspractical application to enable one skilled in the art to utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

What is claimed is:
 1. A method to select a transmission scheme for aradio frequency (RF) burst between a servicing base station andindividual wireless terminals in a cellular wireless communicationsystem, the method comprising: implementing a first transmission schemebetween the servicing base station and the wireless terminal; receivinga first downlink quality report corresponding to the first transmissionscheme at the servicing base station from the wireless terminal, whereinthe downlink quality report comprises: a bit error probability (BEP)based on a re-encoded bit error (RBER) of data within the RF bursts andan estimated BEP derived from a signal to noise ratio (SNR) of the RFburst; and/or a block error rate (BLER) of data within the RF bursts;comparing the first downlink quality report corresponding to the firsttransmission scheme to at least one link adaptation threshold forindividual wireless terminals; implementing an alternative transmissionscheme between the servicing base station and the wireless terminal whenthe first downlink quality report compares unfavorably to the at leastone link adaptation threshold, and wherein the alternative transmissionscheme is expected to result in an expected quality report beingimproved over the first downlink quality report; and adjusting the atleast one link adaptation threshold at the servicing base station forindividual wireless terminals based on the downlink quality report. 2.The method of claim 1, wherein the BLER is derived from a bitmapreported by the wireless terminal.
 3. The method of claim 2, wherein thedownlink quality report further comprises: a mean BLER determined byaveraging together the BLER of each RF burst within a data frame; and astandard deviation of the BLER within the data frame.
 4. The method ofclaim 3, wherein the wireless terminal determines the BEP based on: anestimated BEP derived from the SNR of the RF burst when the data withinthe RF burst decoded unfavorably; and the estimated BEP, the RBER,and/or BLER when the data within the RF burst decoded favorably.
 5. Themethod of claim 4, wherein the SNR is derived from a training sequencewithin the RF burst.
 6. The method of claim 4, wherein the SNR maps tothe estimated BEP based on a modulation format of the RF bursts.
 7. Themethod of claim 6, wherein the modulation format of the RF burst is GMSKor 8PSK.
 8. The method of claim 3, wherein decoding unfavorablycorresponds to the data within the RF burst having a measured bit errorrate (BER) exceeding a predetermined threshold value, and wherein theestimated BEP considers the measured BER at the predetermined thresholdvalue or greater.
 9. The method of claim 8, wherein the predeterminedthreshold value is based on a Coding Scheme of the RF burst.
 10. Themethod of claim 2, wherein adjusting the at least one link adaptationthreshold at the servicing base station for individual wirelessterminals based on the downlink quality report further comprises:incrementing the at least one link adaptation threshold when anunfavorable downlink quality report is received at the servicing basestation; and decrementing the at least one link adaptation thresholdwhen a favorable downlink quality report is received at the servicingbase station.
 11. The method of claim 10, wherein: an unfavorabledownlink quality report comprises an unfavorable comparison between theBLER and a BLER threshold; and a favorable downlink quality reportcomprises a favorable comparison between the BLER and the BLERthreshold.
 12. The method of claim 1, further comprising dynamicallyselecting a transmission scheme for a radio frequency (RF) burst betweena servicing base station and a non-wireless terminal in a cellularwireless communication system using the downlink quality report of thewireless terminal.
 13. A cellular wireless communication system thatcomprises: at least one servicing base station operable to select atransmission scheme for a radio frequency (RF) burst between the atleast one servicing base station and at least one wireless terminal; atleast one wireless terminal operable to transmit a downlink qualityreport on the transmission scheme, wherein the downlink quality reportcomprises: a bit error probability (BEP) based on a re-encoded bit error(RBER) of data within the RF burst and an estimated BEP derived from asignal to noise ratio (SNR) of the RF burst; and/or a block error rate(BLER) of data within the RF bursts; a link adaptation system operablycoupled to the at least one servicing base station operable to: comparethe downlink quality report to at least one link adaptation threshold ofthe at least one wireless terminal; implement an alternativetransmission scheme between the at least one servicing base station andthe at least one wireless terminal when the downlink quality reportcompares unfavorably to the at least one link adaptation threshold, andwherein the alternative transmission scheme is expected to result in anexpected downlink quality report being improved over the downlinkquality report; and adjust the at least one link adaptation threshold atthe servicing base station for individual wireless terminals based onthe downlink quality report.
 14. The cellular wireless communicationsystem of claim 13, wherein the BLER is derived from a bitmap reportedby the wireless terminal.
 15. The cellular wireless communication systemof claim 13, wherein the downlink quality report further comprises: amean BLER determined by averaging together the BLER of each RF burstwithin a data frame; and a standard deviation of the BLER within thedata frame.
 16. The cellular wireless communication system of claim 15,wherein the at least one wireless terminal determines the BEP based on:an estimated BEP derived from the SNR of the RF burst when the datawithin the RF burst decoded unfavorably; and the estimated BEP, theRBER, and or BLER when the data within the RF burst decoded favorably.17. The cellular wireless communication system of claim 16, wherein theSNR is derived from a training sequence within the RF burst.
 18. Thecellular wireless communication system of claim 17, wherein the SNR mapsto the estimated BEP based on a modulation format of the RF burst. 19.The cellular wireless communication system of claim 18, wherein themodulation format of the RF burst is GMSK or 8PSK.
 20. The cellularwireless communication system of claim 15, wherein decoding unfavorablycorresponds to the data within the RF burst having a measured bit errorrate (BER) exceeding a predetermined threshold value, and wherein theestimated BEP considers the measured BER at the predetermined thresholdvalue or greater.
 21. The cellular wireless communication system ofclaim 20, wherein the predetermined threshold value is based on a CodingScheme of the RF burst.
 22. The cellular wireless communication systemof claim 15, wherein: the at least one link adaptation threshold isincremented when an unfavorable downlink quality report is received atthe servicing base station; and the at least one link adaptationthreshold is decremented when a favorable downlink quality report isreceived at the servicing base station.
 23. The cellular wirelesscommunication system of claim 13, wherein the wireless terminal operatesaccording to the GSM standard.
 24. A method to dynamically select atransmission scheme for a radio frequency (RF) burst between a servicingbase station and individual wireless terminals in a cellular wirelesscommunication system, the method comprising: implementing a firsttransmission scheme between the servicing base station and the wirelessterminal; receiving a first downlink quality report corresponding to thefirst transmission scheme at the servicing base station from thewireless terminal, wherein the downlink quality report comprises: ablock error rate (BLER) of data within the RF bursts; a mean bit errorprobability (BEP) determined by averaging a BEP of each RF burst withina data frame; and a standard deviation of the BEP within the data frame,wherein the BEP is based on an estimated BEP derived from a signal tonoise ratio (SNR) of the RF burst and a re-encoded bit error (RBER),wherein: the estimated BEP is weighed more heavily when data within RFburst is decoded unfavorably; the RBER corresponds to a bit error rate(BER) exceeding a threshold value when data within RF burst is decodedunfavorably; and the RBER is weighed more heavily when data within RFburst is decoded favorably. comparing the first downlink quality reportcorresponding to the first transmission scheme to at least one linkadaptation threshold; and implementing an alternative transmissionscheme between the servicing base station and the wireless terminal whenthe downlink quality report compares unfavorably to the at least onelink adaptation threshold, and wherein alternative transmission schemeis expected to result in an expected quality report being improved overthe first downlink quality report; and adjusting the at least one linkadaptation threshold at the servicing base station for individualwireless terminals based on the downlink quality report.
 25. The methodof claim 24, wherein the SNR is derived from a training sequence withinthe RF burst.
 26. The method of claim 25, wherein the transmissionscheme comprises: a coding scheme; and a modulation format.
 27. Themethod of claim 26, wherein the SNR maps to the estimated BEP based on amodulation format of the RF burst.
 28. The method of claim 27, whereinthe modulation format of the RF burst is GMSK or 8PSK.
 29. The method ofclaim 24, wherein: the at least one link adaptation threshold isincremented when an unfavorable downlink quality report is received atthe servicing base station; and the at least one link adaptationthreshold is decremented when a favorable downlink quality report isreceived at the servicing base station.
 30. The method of claim 24,wherein the wireless terminal operates according to the GSM standard.